Various electron tubes have been proposed. The electron tube have a photocathode that emits photoelectrons in response to an incident light and an electron-bombarded semiconductor device, such as an avalanche photodiode (hereinafter, referred to as APD) that amplifies the photoelectrons so as to detect them.
As an electron tube using the APD, there has been proposed an electron tube having an entrance window inside of which a photocathode is formed and a conductive stem on which the APD is disposed. The entrance window is provided at the opening of an insulating container, and the conductive stem is provided opposed to the photocathode of the insulating container. A signal output from the APD is input to an electrical circuit provided outside the insulating container through a lead pin and thereby the incident electrons are detected. The electrical circuit includes a capacitor and an amplifier (refer to, for example, Patent Document 1).
Further, as to the above-described electron tube, there has also been proposed an electron tube in which the conductive stem protrudes inside of the insulating container. Also in this case, the electrical circuit that detects the incident electrons is provided outside the conductive stem and insulating container (refer to, for example, Patent Document 2).
[Patent Document 1]
Japanese Patent Application Laid-Open Publication No. 9-312145 (pages 3 to 6, FIG. 1)
[Patent Document 2]
Japanese Patent Application Laid-Open Publication No. 9-297055 (pages 4 to 9, FIG. 4)